Reading and comparing algorithms

Questions 1 to 5 of 8

1. 1. The loop for the sum of 1 to n makes one addition for each number from 1 to n. It makes 1,000 additions when n is 1,000. How many additions does it make when n is 250,000?

   Type a number.

2. 2. The loop for the sum of the even numbers from 1 to n checks every number and adds only the even ones. For n equal to 100, how many checks and how many additions does it make?

   100 checks and 100 additions100 checks and 50 additions50 checks and 100 additions3 checks and 50 additions
3. 3. The function mystery is below. Why does mystery([-4, -1, -7]) return 0? ``python def mystery(values): result = 0 pos = 0 while pos < len(values) and values[pos] != 0: if values[pos] > result: result = values[pos] pos = pos + 1 return result ``

   Because the loop stops at the first negative numberBecause pos starts at 1 and skips the first valueBecause RETURN runs before the loopBecause result starts at 0, and no value is bigger than 0, so result never changes
4. 4. In find_first_repeat, the check items[i] in seen comes before seen.append(items[i]). Why must the order stay this way?

   Because seen must hold the answer before the loop startsBecause the check is faster when seen is shortBecause otherwise every item would be found in seen right after it is added, so the first item would stop the loopBecause found is read by the check, and must be set first
5. 5. True or false: a formula that gives the right answer for n equal to 10 is proven correct for every n.

   True, because the answer for n = 10 is enough to check any formulaFalse, because a formula right at one size can still be wrong at others, so test it against the loop for many small inputs